Motor

ABSTRACT

A motor includes a rotating portion. The rotating portion includes a shaft, a rotor hub, and a flywheel. The rotor hub is arranged to extend in an annular shape around the shaft. The flywheel is arranged axially above the rotor hub. The rotating portion of the motor includes an annular inertia portion. The inertia portion is arranged to have a specific gravity greater than a specific gravity of the flywheel. At least a portion of the inertia portion and at least a portion of the radial bearing portion are arranged to radially overlap with each other. The inertia portion having the specific gravity greater than the specific gravity of the flywheel is arranged at a position radially overlapping with the radial bearing portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor.

2. Description of the Related Art

A disk drive apparatus, such as, for example, a hard disk drive, istypically equipped with a motor (i.e., an FDB motor) including a fluiddynamic bearing. In the FDB motor, a lubricating oil is arranged betweena sleeve of a stationary portion and a shaft of a rotating portion. Adynamic pressure groove is defined in an inner circumferential surfaceof the sleeve or an outer circumferential surface of the shaft, andwhile the motor is running, the dynamic pressure groove induces adynamic pressure in the lubricating oil. This allows the rotatingportion including the shaft to rotate with high precision.

Thus, in recent years, FDB motors have sometimes been used also inapplications other than disk drive apparatuses. However, when the FDBmotor is used in an application other than the disk drive apparatus, anadditional component, such as, for example, a flywheel, is sometimesattached to the rotating portion of the FDB motor. Such an additionalcomponent changes the axial height of the rotating portion. If the axialheight of the rotating portion becomes high, the runout of the rotatingportion becomes significant while the motor is running, which makes itdifficult to stabilize the posture of the rotating portion.

SUMMARY OF THE INVENTION

A motor according to a preferred embodiment of the present inventionincludes a stationary portion and a rotating portion. The rotatingportion is supported to be rotatable about a central axis extending in avertical direction with respect to the stationary portion. The rotatingportion includes a shaft, a rotor hub, a flywheel, and an inertiaportion. The shaft is arranged to extend along the central axis. Therotor hub is arranged to extend in an annular shape around the shaft.The flywheel is arranged axially above the rotor hub. The inertiaportion is an annular member and is arranged to have a specific gravitygreater than a specific gravity of the flywheel. The stationary portionincludes a sleeve arranged to rotatably support the shaft. The motorincludes a radial bearing portion where the sleeve and the shaft arearranged radially opposite to each other with a lubricating oil arrangedtherebetween. At least a portion of the inertia portion and at least aportion of the radial bearing portion are arranged to radially overlapwith each other.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of a motor according to afirst preferred embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view of a motor according to asecond preferred embodiment of the present invention.

FIG. 3 is a partial vertical cross-sectional view illustrating a joiningportion and its vicinity according to the second preferred embodiment ofthe present invention.

FIG. 4 is a partial vertical cross-sectional view of the motor accordingto the second preferred embodiment of the present invention.

FIG. 5 is a vertical cross-sectional view of a sleeve according to thesecond preferred embodiment of the present invention.

FIG. 6 is a bottom view of the sleeve according to the second preferredembodiment of the present invention.

FIG. 7 is a partial vertical cross-sectional view of a motor accordingto an example modification of the present invention.

FIG. 8 is a partial vertical cross-sectional view of a motor accordingto another example modification of the present invention.

FIG. 9 is a partial vertical cross-sectional view of a motor accordingto still another example modification of the present invention.

FIG. 10 is a partial vertical cross-sectional view of a motor accordingto yet another example modification of the present invention.

FIG. 11 is a partial vertical cross-sectional view of a motor accordingto yet another example modification of the present invention.

FIG. 12 is a partial vertical cross-sectional view of a motor accordingto yet another example modification of the present invention.

FIG. 13 is a vertical cross-sectional view of a motor according to yetanother example modification of the present invention.

FIG. 14 is a vertical cross-sectional view of a motor according to yetanother example modification of the present invention.

FIG. 15 is a partial vertical cross-sectional view of a motor accordingto yet another example modification of the present invention.

FIG. 16 is a partial vertical cross-sectional view of a motor accordingto yet another example modification of the present invention.

FIG. 17 is a partial vertical cross-sectional view of a motor accordingto yet another example modification of the present invention.

FIG. 18 is a partial vertical cross-sectional view of a motor accordingto yet another example modification of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, motors according to preferred embodiments will bedescribed. It is assumed herein that a direction parallel to a centralaxis of a motor is referred to by the term “axial direction”, “axial”,or “axially”, that directions perpendicular to the central axis of themotor are each referred to by the term “radial direction”, “radial”, or“radially”, and that a direction along a circular arc centered on thecentral axis of the motor is referred to by the term “circumferentialdirection”, “circumferential”, or “circumferentially”. It is alsoassumed herein that an axial direction is a vertical direction, and thata side on which a flywheel is arranged with respect to a rotor hub is anupper side, and the shape of each member or portion and relativepositions of different members or portions will be described based onthe above assumptions. It should be noted, however, that the abovedefinitions of the vertical direction and the upper and lower sides arenot meant to restrict in any way the orientation of a motor according toany preferred embodiment of the present invention at the time ofmanufacture or when in use.

FIG. 1 is a vertical cross-sectional view of a motor 1A according to afirst preferred embodiment of the present invention. Referring to FIG.1, the motor 1A includes a stationary portion 2A and a rotating portion3A. The rotating portion 3A is supported to be rotatable about a centralaxis 9A with respect to the stationary portion 2A.

The rotating portion 3A includes a shaft 31A, a rotor hub 32A, and aflywheel 35A. The shaft 31A is arranged to extend along the central axis9A. The rotor hub 32A is arranged to extend in an annular shape aroundthe shaft 31A. The flywheel 35A is arranged axially above the rotor hub32A.

The stationary portion 2A includes a sleeve 24A arranged to rotatablysupport the shaft 31A. The motor 1A includes a radial bearing portion51A. At the radial bearing portion 51A, the sleeve 24A and the shaft 31Aare arranged radially opposite to each other with a lubricating oil 50Aarranged therebetween.

The rotating portion 3A of the motor 1A includes an annular inertiaportion 36A. The inertia portion 36A rotates together with the rotor hub32A and the flywheel 35A while the motor 1A is running. The inertiaportion 36A is arranged to have a specific gravity greater than aspecific gravity of the flywheel 35A.

Referring to FIG. 1, at least a portion of the inertia portion 36A andat least a portion of the radial bearing portion 51A are arranged toradially overlap with each other. That is, the inertia portion 36Ahaving the specific gravity greater than the specific gravity of theflywheel 35A is arranged at the position radially overlapping with theradial bearing portion 51A. This leads to a stable posture of therotating portion 3A having the flywheel 35A during rotation.

FIG. 2 is a vertical cross-sectional view of a motor 1 according to asecond preferred embodiment of the present invention. Referring to FIG.2, the motor 1 includes a stationary portion 2 and a rotating portion 3.The rotating portion 3 is supported to be rotatable about a central axis9 extending in a vertical direction with respect to the stationaryportion 2.

The stationary portion 2 preferably includes a mounting plate 21, astator holder 22, a stator 23, and a sleeve 24.

The mounting plate 21 is a plate-shaped member arranged to support thestator holder 22. A metal, such as, for example, stainless steel, isused as a material of the mounting plate 21. The mounting plate 21 isarranged to be substantially perpendicular to the central axis 9. Themounting plate 21 includes a through hole 210 including an opening edgewhich is circular in a plan view. A lower end portion of the statorholder 22 is fitted in the through hole 210. When the motor 1 is fittedto a device or the like, the mounting plate 21 is fixed to a frame ofthe device or the like through, for example, screws. Note that a circuitboard to supply electric drive currents to coils 42 of the stator 23,which will be described below, may be arranged on a surface of themounting plate 21.

The stator holder 22 is a substantially cylindrical member extending inthe axial direction. The lower end portion of the stator holder 22 isinserted into the through hole 210, and is fixed to the mounting plate21 preferably by crimping. Note, however, that the stator holder 22 mayalternatively be fixed to the mounting plate 21 by another method, suchas, for example, welding. Also note that the mounting plate 21 and thestator holder 22 may alternatively be defined by a single continuousmonolithic member.

The stator 23 includes a stator core 41 and the coils 42. The statorcore 41 is defined by, for example, laminated steel sheets, each ofwhich is a magnetic body. The stator core 41 includes an annular coreback 411 and a plurality of teeth 412. The stator holder 22 is insertedinto a through hole of the core back 411. The core back 411 is fixed toan outer circumferential surface of the stator holder 22. The core back411 is fixed to the stator holder 22 through, for example, pressfitting, adhesion, or the like. The teeth 412 are arranged to projectradially outward from the core back 411. A surface of the stator core41, including the teeth 412, is coated with an insulating coating. Aconducting wire is wound around each of the teeth 412 to define thecoils 42. Note that, in place of the insulating coating, an insulatormade of a resin may be arranged between the teeth 412 and the coils 42.Also note that the stator core 41 may alternatively be defined by a dustcore.

The sleeve 24 is a member arranged to rotatably support a shaft 31,which will be described below. The sleeve 24 is a substantiallycylindrical member, and is arranged to extend in the axial directionaround the shaft 31. A lower portion of the sleeve 24 is inserted into aspace radially inside the stator holder 22, (i.e., into a through holeof the stator holder 22), and is fixed to the stator holder 22 through,for example, an adhesive. An upper end portion of the sleeve 24 isarranged axially above both an upper end portion of the stator holder 22and an upper end portion of the stator 23. An opening at a lower endportion of the sleeve 24 is closed by a disk-shaped cap 25.

The rotating portion 3 preferably includes the shaft 31, a rotor hub 32,a yoke 33, a magnet 34, a flywheel 35, and an inertia portion 36.

The shaft 31 is a columnar member arranged to extend along the centralaxis 9. A metal, such as, for example, stainless steel, is used as amaterial of the shaft 31. A lower end portion of the shaft 31 isarranged radially inside of the sleeve 24 (i.e., in a through hole ofthe sleeve 24). An upper end portion 311 of the shaft 31 is arrangedaxially above the upper end portion of the sleeve 24. An outercircumferential surface of the shaft 31 is arranged radially opposite toan inner circumferential surface of the sleeve 24 with a slight gaptherebetween.

An annular thrust plate 37 is fixed to the lower end portion of theshaft 31. The thrust plate 37 is arranged to extend radially outwardfrom a lower end of the shaft 31. An upper surface of the thrust plate37 is arranged axially opposite to a lower surface of the sleeve 24 witha slight gap therebetween. A lower surface of the thrust plate 37 isarranged axially opposite to an upper surface of the cap 25 with aslight gap therebetween.

The rotor hub 32 is arranged to extend in an annular shape around theshaft 31. A metal, such as, for example, an aluminum alloy, is used as amaterial of the rotor hub 32. Referring to FIG. 2, the rotor hub 32preferably includes a joining portion 321, a cylindrical portion 322,and a flange portion 323. The joining portion 321 is arranged at aradially innermost portion of the rotor hub 32, and is fixed to theouter circumferential surface of the shaft 31. The joining portion 321is arranged axially above a radial bearing portion 51, which will bedescribed below. A through hole 320 passing through the rotor hub 32 inthe axial direction is defined radially inside the joining portion 321.The upper end portion 311 of the shaft 31 is press fitted in the throughhole 320 of the rotor hub 32.

FIG. 3 is a partial vertical cross-sectional view illustrating thejoining portion 321 and its vicinity. Referring to FIG. 3, an adhesive38 is arranged between an outer circumferential surface of the upper endportion 311 of the shaft 31 and an inner circumferential surface of thejoining portion 321. In the motor 1, the shaft 31 and the rotor hub 32are fixed to each other through press fitting and the adhesive 38. Note,however, that the shaft 31 and the rotor hub 32 may alternatively befixed to each other through only press fitting or through only theadhesive 38. Also note that the shaft 31 and the rotor hub 32 mayalternatively be fixed to each other by another method, such as, forexample, shrink fitting.

Referring to FIG. 2, the cylindrical portion 322 is cylindrical, and isarranged to extend in the axial direction. The cylindrical portion 322is arranged radially outward of the joining portion 321 and radiallyinward of the inertia portion 36, which will be described below. Theflange portion 323 is arranged to extend radially outward from a lowerend portion of the cylindrical portion 322. The flange portion 323 isarranged axially below the inertia portion 36.

The yoke 33 is a cylindrical member arranged to hold the magnet 34. Theyoke 33 is arranged to be coaxial or substantially coaxial with thecentral axis 9. A magnetic material, such as, for example, iron, is usedas a material of the yoke 33. An upper end portion of the yoke 33 isfixed to a lower surface of the flange portion 323 of the rotor hub 32through, for example, an adhesive, crimping, or the like.

The magnet 34 is fixed to the inner circumferential surface of the yoke33 through, for example, an adhesive or the like. In the motor 1, anannular permanent magnet is used as the magnet 34. The magnet 34 is asubstantially cylindrical member arranged radially outside the stator23. An inner circumferential surface of the magnet 34 includes north andsouth poles arranged to alternate with each other in the circumferentialdirection. Moreover, the inner circumferential surface of the magnet 34is arranged radially opposite to radially outer end surfaces of theteeth 412 with a slight gap therebetween. That is, the magnet 34 has amagnetic pole surface arranged radially opposite to the stator 23. Note,however, that the magnet 34 may not necessarily be annular, and that aplurality of magnets may alternatively be used in place of the magnet34. In the case where a plurality of magnets are used, a plurality ofmagnets 34 are arranged on the inner circumferential surface of the yoke33 such that north and south poles alternate with each other in thecircumferential direction.

Once the electric drive currents are supplied to the coils 42, arotating magnetic field is generated in the teeth 412. Interactionbetween magnetic flux of the teeth 412 and magnetic flux of the magnet34 produces a circumferential torque. This allows the rotating portion3, including the magnet 34, to rotate about the central axis 9.

The flywheel 35 is arranged axially above the rotor hub 32. The flywheel35 is fixed to the rotor hub 32 through, for example, an adhesive.Accordingly, the flywheel 35 rotates together with the rotor hub 32while the motor 1 is running. An ABS resin, which is a thermoplasticresin, for example, is used as a material of the flywheel 35. Note that,instead of the ABS resin, another material, such as, for example, athermosetting resin or a metal, may alternatively be used as thematerial of the flywheel 35. The flywheel 35 is able to achieve a lowerweight when the flywheel 35 is made of a resin than when the flywheel 35is made of a metal. Use of a resin for the flywheel 35 therefore leadsto reducing a load during rotation of the motor 1.

In the motor 1, the flywheel 35 is arranged to have a circular externalshape when viewed in the axial direction with the central axis 9 as acenter. This circular external shape of the flywheel 35 contributes toreducing swinging of the rotating portion 3 while the motor 1 isrunning.

Next, a fluid dynamic bearing mechanism 5 included in the motor 1 willnow be described below. FIG. 4 is a partial vertical cross-sectionalview of the motor 1. Referring to FIG. 4, the lubricating oil 50 isarranged between a combination of the sleeve 24 and the cap 25 and acombination of the shaft 31 and the thrust plate 37. A polyolester oilor a diester oil, for example, is used as the lubricating oil 50.

FIG. 5 is a vertical cross-sectional view of the sleeve 24. Referring toFIG. 5, the inner circumferential surface of the sleeve 24 includes anupper radial groove array 511 and a lower radial groove array 512. Thelower radial groove array 512 is arranged axially below the upper radialgroove array 511. Each of the upper and lower radial groove arrays 511and 512 is a groove array arranged in a so-called herringbone pattern.While the motor 1 is running, the upper and lower radial groove arrays511 and 512 induce a dynamic pressure in a portion of the lubricatingoil 50 which is present between the inner circumferential surface of thesleeve 24 and the outer circumferential surface of the shaft 31. Thisproduces a radial supporting force between the sleeve 24 and the shaft31.

That is, in the motor 1, the inner circumferential surface of the sleeve24 is arranged radially opposite to the outer circumferential surface ofthe shaft 31 with the lubricating oil 50 arranged therebetween. Theradial bearing portion 51 is thus defined. The radial bearing portion 51includes an upper radial bearing portion 501 arranged to generate adynamic pressure through the upper radial groove array 511, and a lowerradial bearing portion 502 arranged to generate a dynamic pressurethrough the lower radial groove array 512. The lower radial bearingportion 502 is arranged axially below the upper radial bearing portion501. Note that each of the upper and lower radial groove arrays 511 and512 is defined in at least one of the inner circumferential surface ofthe sleeve 24 and the outer circumferential surface of the shaft 31.Also note that the number of radial dynamic pressure groove arrays mayalternatively be one or more than two.

FIG. 6 is a bottom view of the sleeve 24. Referring to FIG. 6, thesleeve 24 includes a thrust groove array 521 in the lower surfacethereof. The thrust groove array 521 includes a plurality of thrustgrooves arranged in the circumferential direction. Each thrust groove isarranged to extend radially in a spiral shape. Note that the thrustgroove array 521 may alternatively be arranged in a herringbone pattern.While the motor 1 is running, the thrust groove array 521 induces adynamic pressure in a portion of the lubricating oil 50 which is presentbetween the lower surface of the sleeve 24 and the upper surface of thethrust plate 37. This produces an axial supporting force between thesleeve 24 and the thrust plate 37.

That is, in the motor 1, the lower surface of the sleeve and the uppersurface of the thrust plate 37 are arranged axially opposite to eachother with the lubricating oil 50 arranged therebetween. A thrustbearing portion 52 is thus defined. Note that the thrust groove array521 is defined in at least one of the lower surface of the sleeve 24 andthe upper surface of the thrust plate 37. Also note that the number ofthrust bearing portions 52 may be two or more. The thrust bearingportion 52 may be defined between the upper surface of the cap 25 andthe lower surface of the thrust plate 37.

A gap including the radial bearing portion 51 and the thrust bearingportion 52 is defined between the combination of the sleeve 24 and thecap 25 and the combination of the shaft 31 and the thrust plate 37. Thisgap is continuously filled with the lubricating oil 50. A liquid surfaceof the lubricating oil 50 is defined between the outer circumferentialsurface of the shaft 31 and the inner circumferential surface of thesleeve 24 in the vicinity of the upper end portion of the sleeve 24. Thefluid dynamic bearing mechanism 5 of the motor 1 is arranged to have aso-called full-fill structure. The fluid dynamic bearing mechanism 5 ofthe motor 1 according to this preferred embodiment includes only oneliquid surface of the lubricating oil 50. The full-fill structure of thefluid dynamic bearing mechanism 5 contributes to reducing swinging ofthe rotating portion 3 due to the orientation of the motor 1 installed,a vibration, and/or the like.

Referring to FIGS. 2 and 4, the rotating portion 3 of the motor 1includes the annular inertia portion 36. The inertia portion 36 isarranged radially outside the cylindrical portion 322, axially above theflange portion 323, and axially below the flywheel 35. The lower surfaceof the inertia portion 36 is arranged to be in contact with the uppersurface of the flange portion 323. The inertia portion 36 is fixed tothe rotor hub 32 through, for example, an adhesive or the like.Accordingly, the inertia portion 36 rotates together with the rotor hub32 and the flywheel 35 while the motor 1 is running.

A metal, such as, for example, stainless steel, is used as the materialof the inertia portion 36. The inertia portion 36 is arranged to havethe specific gravity greater than the specific gravity of the flywheel35. The inertia portion 36 fixed to the rotating portion 3 thereforeincreases the inertial force of the rotating portion 3 when the motor 1is running. This leads to stabilizing the posture of the rotatingportion 3 when the rotating portion 3 is rotating. In particular, in themotor 1, the inertia portion 36 is arranged to have the total massgreater than the total mass of the flywheel 35. This leads to a morestable posture of the rotating portion 3 during rotation. Note that theinertia portion 36 may not necessarily be arranged to have the totalmass greater than the total mass of the flywheel 35. That is, theinertia portion 36 may alternatively be arranged to have the total masssmaller than the total mass of the flywheel 35.

Referring to FIGS. 2 and 4, in the motor 1, at least a portion of theinertia portion 36 and at least a portion of the radial bearing portion51 are arranged to radially overlap with each other. Specifically, atleast a portion of the inertia portion 36 and at least a portion of theupper and lower radial bearing portions 501 and 502 are arranged toradially overlap with each other. More specifically, referring to FIG.4, a lower portion of an axial range A1 in which the inertia portion 36extends is arranged to overlap with an upper portion of an axial rangeA2 in which the upper radial bearing portion 501 extends. Accordingly,the upper radial bearing portion 501 supports the rotating portion 3 atan axial position close to the inertia portion 36, which has a largespecific gravity. This leads to a stable posture of the rotating portion3 when the motor 1 is running.

Referring to FIG. 5, in the motor 1, an axial dimension h1 of the upperradial groove array 511 is arranged to be greater than an axialdimension h2 of the lower radial groove array 512. Therefore, an axialdimension of the upper radial bearing portion 501 is greater than anaxial dimension of the lower radial bearing portion 502. At least aportion of the inertia portion 36 and at least a portion of the upperradial bearing portion 501 are arranged to radially overlap with eachother. This causes the lubricating oil 50 to generate a greater dynamicpressure at a position radially overlapping with the inertia portion 36.This leads to a more stable posture of the rotating portion 3 when themotor 1 is running.

In the motor 1, the lower surface of the inertia portion 36 is arrangedto be in contact with the upper surface of the flange portion 323. Thisreduces deviating the axial position of the inertia portion 36. In themotor 1, the inertia portion 36 is arranged above the flange portion 323and below the flywheel 35. That is, the inertia portion 36 is sandwichedbetween the rotor hub 32 and the flywheel 35. This further reducesdeviating the axial position of the inertia portion 36. The reduction inaxial positional deviation of the inertia portion 36 reduces incliningthe inertia portion 36. This leads to a more stable posture of therotating portion 3 when the motor 1 is running.

While exemplary preferred embodiments of the present invention has beendescribed above, it will be understood that the present invention is notlimited to the above-described preferred embodiments.

FIG. 7 is a partial vertical cross-sectional view of a motor 1Baccording to an example modification of the present invention. Aflywheel 35B in FIG. 7 is a resin-molded article produced with aninertia portion 36B as an insert. That is, a molten resin is poured intoa cavity of a mold with the inertia portion 36B arranged in the mold,and the resin is cured to mold the flywheel 35B. This achieves themolding of the flywheel 35B and the fixing of the flywheel 35B to theinertia portion 36B at the same time. Thus, a reduction in the number ofprocesses to manufacture the motor 1B is achieved. Moreover, theflywheel 35B and the inertia portion 36B are fixed to each other withincreased strength.

FIG. 8 is a partial vertical cross-sectional view of a motor 1Caccording to another example modification of the present invention. Aflywheel 35C in FIG. 8 includes a cylindrical wall portion 351C arrangedto extend axially downward from an outer circumferential portionthereof. The wall portion 351C is arranged to cover at least a portionof an outer circumferential surface of an inertia portion 36C. That is,an upper end portion of the inertia portion 36C is fitted radiallyinside of the wall portion 351C. In other words, the upper end portionof the inertia portion 36C is fitted in a through hole defined by aninside surface of the wall portion 351C. This reduces the likelihoodthat relative positions of the flywheel 35C and the inertia portion 36Cwill be disturbed. This contributes to further reducing swinging of arotating portion 3C while the motor 1C is running.

Note that the wall portion 351C may not necessarily be cylindrical. Forexample, the flywheel 35C may include a plurality of arc-shaped wallportions arranged in the circumferential direction in place of thecylindrical wall portion 351C.

FIG. 9 is a partial vertical cross-sectional view of a motor 1Daccording to still another example modification of the presentinvention. A flywheel 35D in FIG. 9 includes a cylindrical wall portion351D arranged to extend axially downward from an outer circumferentialportion thereof. The wall portion 351D is arranged to cover an outercircumferential surface of an inertia portion 36D from an upper end to alower end thereof. In addition, the wall portion 351D is arranged tocover at least a portion of an outer circumferential surface of a rotorhub 32D. That is, both the inertia portion 36D and the rotor hub 32D arefitted radially inside of the wall portion 351D. In other words, boththe inertia portion 36D and the rotor hub 32D are fitted in a throughhole defined by an inside surface of the wall portion 351D. This reducesthe likelihood that relative positions of the flywheel 35D, the inertiaportion 36D, and the rotor hub 32D will be disturbed. This contributesto further reducing swinging of a rotating portion 3D while the motor 1Dis running.

Note that the wall portion 351D may not necessarily be cylindrical. Forexample, the flywheel 35D may include a plurality of arc-shaped wallportions arranged in the circumferential direction in place of thecylindrical wall portion 351D.

In the example modification illustrated in FIG. 9, an outside radius r1of the flywheel 35D is arranged to be greater than an outside radius r2of the rotor hub 32D. When the radius r1 of the flywheel 35D is large asdescribed above, a swing of the rotating portion 3D tends to more easilyoccur while the motor 1D is running. However, in this motor 1D, a center30D of gravity of the rotating portion 3D is arranged at a levelequivalent to the level of a joining portion 321D. This contributes topreventing a swing of the rotating portion 3D from causing damage, suchas, for example, a rupture, to the joining portion 321D.

FIG. 10 is a partial vertical cross-sectional view of a motor 1Eaccording to yet another example modification of the present invention.In the example modification illustrated in FIG. 10, an axial dimensionh3 of a flywheel 35E is greater than an axial distance h4 from a lowerend surface of a stationary portion 2E to an upper end surface of arotor hub 32E. When the axial dimension h3 of the flywheel 35E is largeas described above, a swing of a rotating portion 3E tends to moreeasily occur while the motor 1E is running. However, in this motor 1E, acenter 30E of gravity of the rotating portion 3E is arranged at a levelequivalent to the level of a joining portion 321E. This contributes tomore effectively preventing a swing of the rotating portion 3E fromcausing damage, such as, for example, a rupture, to the joining portion321E.

FIG. 11 is a partial vertical cross-sectional view of a motor 1Faccording to yet another example modification of the present invention.A rotating portion 3F in FIG. 11 includes a rotating member 39F. Therotating member 39F is a single continuous monolithic member including arotor hub 32F and an inertia portion 36F. A metal, such as, for example,an aluminum alloy, is used as a material of the rotating member 39F. Thenumber of parts of the motor 1F can thus be reduced when compared to thecase where a rotor hub and an inertia portion are produced separately.In addition, there is not a need for an operation of fixing the inertiaportion 36F to the rotor hub 32F. This reduces the number of processesto manufacture the motor 1F.

In the example modification illustrated in FIG. 11, the rotating member39F has a recess portion 391F arranged between the rotor hub 32F and theinertia portion 36F. The recess portion 391F extends downward from anupper surface of the rotor hub 32F. Accordingly, a cylindrical portion322F of the rotor hub 32F extends axially while being spaced apart fromthe inertia portion 36F at the axially inside thereof. A flange portion323F of the rotor hub 32F extends radially outward from the cylindricalportion 322F axially below the recess portion 391F and the inertiaportion 36F.

A flywheel 35F has a protrusion portion 352F arranged to protrudedownward from a lower end thereof. The protrusion portion 352F isarranged in the recess portion 391F. That is, the protrusion portion352F is fitted in the recess portion 391F. Accordingly, at least aportion of the protrusion portion 352F is arranged to radially overlapwith the cylindrical portion 322F and the inertia portion 36F. In theexample modification illustrated in FIG. 11, as described above, atleast a portion of the rotor hub 32F, at least a portion of the flywheel35F, and at least a portion of the inertia portion 36F are arranged tobe the same level as one another. This leads to a more stable posture ofthe rotating portion 3F when the motor 1F is running.

In the example modification illustrated in FIG. 11, an innercircumferential surface of the protrusion portion 352F is in contactwith an outer circumferential surface of the rotor cylindrical portion322F. This contributes to accurate radial positioning of the flywheel35F with higher precision.

FIG. 12 is a partial vertical cross-sectional view of a motor 1Gaccording to yet another example modification of the present invention.A rotating portion 3G in FIG. 12 includes a rotating member 39G. Therotating member 39G is a single continuous monolithic member including arotor hub 32G and a flywheel 35G. The number of parts of the motor 1Gcan thus be reduced when compared to the case where a rotor hub and aflywheel are produced separately. In addition, there is not a need foran operation of fixing the flywheel 35G to the rotor hub 32G. Thisreduces the number of processes to manufacture the motor 1G. Therotating member 39G may be, for example, a casting or an injectionmolded article produced with an inertia portion 36G as an insert. Thisallows the rotating member 39G and the inertia portion 36G to besecurely fixed to each other while achieving a reduction in the numberof processes to manufacture the motor 1G.

FIG. 13 is a vertical cross-sectional view of a motor 1H according toyet another example modification of the present invention. In theexample modification illustrated in FIG. 13, a rotating portion 3Hincludes a mirror 40H. The mirror 40H is supported by a flywheel 35H.Once the motor 1H is driven, the mirror 40H is caused to rotate togetherwith the flywheel 35H. Accordingly, the motor 1H allows light incidenton the mirror 40H to be reflected while deflecting the light with afixed cycle. Note however that the mirror 40H of the flywheel 35H tendsto cause swinging of the rotating portion 3H. In the examplemodification illustrated in FIG. 13, however, an inertia portion 36H isarranged at a position radially overlapping with a radial bearingportion 51H. This leads to a stable posture of the rotating portion 3Hwhen the motor 1H is running.

FIG. 14 is a vertical cross-sectional view of a motor 1J according toyet another example modification of the present invention. In theexample modification illustrated in FIG. 14, a rotor hub 32J includes anannular portion 324J arranged around an upper end portion of a shaft31J. A lower surface of the annular portion 324J is arranged axiallyopposite to an upper surface of a sleeve 24J with a slight gaptherebetween. In the example modification illustrated in FIG. 14, alubricating oil 50J is arranged also in this gap between the lowersurface of the annular portion 324J and the upper surface of the sleeve24J. A thrust groove array is defined in one of the lower surface of theannular portion 324J and the upper surface of the sleeve 24J. While themotor 1J is running, the thrust groove array induces a dynamic pressurein a portion of the lubricating oil 50J which is present between thelower surface of the annular portion 324J and the upper surface of thesleeve 24J. This produces an axial supporting force between the sleeve24J and the rotor hub 32J.

That is, in the motor 1J illustrated in FIG. 14, the lower surface ofthe annular portion 324J is arranged axially opposite to the uppersurface of the sleeve 24J with the lubricating oil 50J arrangedtherebetween. A thrust bearing portion 52J is thus defined. A gapincluding a radial bearing portion 51J and a thrust bearing portion 52Jis continuously filled with the lubricating oil 50J.

Also in the example illustrated in FIG. 14, an inertia portion 36Jhaving a specific gravity greater than a specific gravity of a flywheel35J is arranged at a position radially overlapping with the radialbearing portion 51J. This leads to a stable posture of a rotatingportion 3J when the motor 1J is running.

FIG. 15 is a partial vertical cross-sectional view of a motor 1Kaccording to yet another example modification of the present invention.In the example modification illustrated in FIG. 15, a yoke 33K has ayoke cylindrical portion 331K and a yoke upper plate portion 332K. Amagnet 34K is fixed to an inner circumferential surface of the yokecylindrical portion 331K. A lower end portion of the yoke cylindricalportion 331K may be arranged above a lower end portion of the magnet 34Kand may be arranged to extend downward of the lower end portion of themagnet 34K. An upper end portion of the yoke cylindrical portion 331K isarranged to extend upward of a flange portion 323K of a rotor hub 32K.Accordingly, the yoke cylindrical portion 331K is arranged to cover atleast a portion of an outer circumferential surface of the magnet 34Kand an entire outer circumferential surface of the rotor hub 32K.

A magnetic material, such as, for example, iron, is used as a materialof the yoke 33K. Therefore, the yoke 33K has a specific gravity greaterthan a specific gravity of the rotor hub 32K. As illustrated in FIG. 15,longer the axial length of the yoke 33K is, greater the mass of the yoke33K is. Accordingly, an inertial force of a rotating portion 3K can beincreased by not only a mass of an inertia portion 36K, but also themass of the yoke 33K. This leads to a more stable posture of therotating portion 3K when the motor 1K is running.

The yoke upper plate portion 332K is a ring-shaped member extendingradially inward from an upper end of the yoke cylindrical portion 331K.A lower surface of the yoke upper plate portion 332K is arranged to bein contact with an upper surface of a flange portion 323K. At the timeof manufacture of the motor 1K, for example, the flange portion 323K ofthe rotor hub 32K is press fitted from below into a radially inner sideof the yoke cylindrical portion 331K. Thereafter, the magnet 34K isinserted into the radially inner side of the yoke cylindrical portion331K, and the inner circumferential surface of the yoke cylindricalportion 331K and the outer circumferential surface of the magnet 34K arefixed to each other through an adhesive.

The yoke upper plate portion 332K and the inertia portion 36K may be incontact with or in non contact with each other. In the exampleillustrated in FIG. 15, the yoke upper plate portion 332K and theinertia portion 36K are in non contact with each other. That is, anaxial cavity is present between the upper surface of the yoke upperplate portion 332K and the lower surface of the inertia portion 36K.This prevents deformation of the yoke 33K by the inertia portion 36K.Accordingly, this prevents the magnet 34K from tilting with respect to acentral axis due to the deformation of the yoke 33K, which reduces aninfluence of the motor 1K on a magnetic circuit.

FIG. 16 is a partial vertical cross-sectional view of a motor 1Maccording to yet another example modification of the present invention.The example modification illustrated in FIG. 16 is different in shape ofa yoke cylindrical portion from the example modification illustrated inFIG. 15. In the example modification illustrated in FIG. 16, an innercircumferential surface of a yoke cylindrical portion 331M includes acylindrical first yoke inner circumferential surface 333M and acylindrical second yoke inner circumferential surface 334M. The firstyoke inner circumferential surface 333M is arranged to be in contactwith an outer circumferential surface of a flange portion 323M of arotor hub 32M. The second yoke inner circumferential surface 334M isarranged below the first yoke inner circumferential surface 333M. Thesecond yoke inner circumferential surface 334M and an outercircumferential surface of a magnet 34M are fixed to each other throughan adhesive.

There is a possibility in that the yoke 33M becomes deformed when therotor hub 32M is press fitted in the yoke 33M. In the examplemodification illustrated in FIG. 16, however, the first yoke innercircumferential surface 333M is arranged radially inward of the secondyoke inner circumferential surface 334M. A step difference 335M isarranged on a boundary between the first yoke inner circumferentialsurface 333M and the second yoke inner circumferential surface 334M.This reduces an influence on the second yoke inner circumferentialsurface 334M even if the first yoke inner circumferential surface 333Mbecomes deformed by press fitting. Moreover, a gap can be securedbetween the second yoke inner circumferential surface 334M and themagnet 34M. Accordingly, the magnet 34M can be arranged radially inwardthe second yoke inner circumferential surface 334M, without being tiltedwith respect to a central axis. In addition, an operation of fixing themagnet 34M to the yoke 33M after the press fitting of the rotor hub 32is facilitated.

FIG. 17 is a partial vertical cross-sectional view of a motor 1Naccording to yet another example modification of the present invention.A flywheel 35N in FIG. 17 includes a cylindrical wall portion 351Narranged to extend axially downward from an outer circumferentialportion thereof. The wall portion in FIG. 17 is different from the wallportion in FIG. 9 in that the wall portion in FIG. 17 is arranged tocover at least a portion of an outer circumferential surface of a yoke33N. In this example modification, a lower surface of an inertia portion36N is fixed to an upper surface of a mounting portion 353N arranged toextend radially outward from a lower end of the wall portion 351N. Notethat the inertia portion 36N may be fixed to an outer circumferentialsurface of the wall portion 351N. In this example modification, at leasta portion of the inertia portion 36N and at least a portion of a lowerradial bearing portion 502N are arranged to radially overlap with eachother. More specifically, an axial range (not illustrated) in which theinertia portion 36N extends is arranged to radially overlap with anaxial range in which the lower radial bearing portion 502N extends. Thisleads to a stable posture of a rotating portion 3N when the motor 1N isrunning.

FIG. 18 is a partial vertical cross-sectional view of a motor 1Oaccording to yet another example modification of the present invention.A flywheel 35O in FIG. 18 includes a cylindrical wall portion 351Oarranged to extend axially downward from an outer circumferentialportion thereof, as in the flywheel illustrated in FIG. 17. A lowersurface of an inertia portion 36O is fixed to an upper surface of amounting portion 353O arranged to extend radially outward from a lowerend of the wall portion 351O. Note that the inertia portion 36O may befixed to an outer circumferential surface of the wall portion 351O. Inthis example modification, at least a portion of the inertia portion 36Oand at least a portion of upper and lower radial bearing portions 501Oand 502O are arranged to radially overlap with each other. When theinertia portion 36O is arranged to radially overlap with an axial rangein which the upper radial bearing portion 501O and the lower radialbearing portion 502O extend, a portion of heavy mass is arranged belowthe motor. This leads to a stable posture of a rotating portion 3O whenthe motor 1O is running.

Note that details of the structure and the shape of a motor according toa preferred embodiment of the present invention may differ from detailsof the structure and the shape of each motor as illustrated in theaccompanying drawings of the present application.

Features of the above-described preferred embodiments and themodifications thereof may be combined appropriately as long as noconflict arises.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A motor comprising: a stationary portion; and arotating portion supported to be rotatable about a central axisextending in a vertical direction with respect to the stationaryportion; wherein the rotating portion includes: a shaft arranged toextend along the central axis; a rotor hub arranged to extend in anannular shape around the shaft; a flywheel arranged axially above therotor hub; and an annular inertia portion arranged to have a specificgravity greater than a specific gravity of the flywheel, the stationaryportion includes a sleeve arranged to rotatably support the shaft, themotor further comprises a radial bearing portion where the sleeve andthe shaft are arranged radially opposite to each other with alubricating oil arranged therebetween, and at least a portion of theinertia portion and at least a portion of the radial bearing portion arearranged to radially overlap with each other.
 2. The motor according toclaim 1, wherein the radial bearing portion includes: an upper radialbearing portion; and a lower radial bearing portion arranged axiallybelow the upper radial bearing portion, and at least a portion of theinertia portion and at least a portion of the upper and lower radialbearing portions are arranged to radially overlap with each other. 3.The motor according to claim 2, wherein an axial dimension of the upperradial bearing portion is greater than an axial dimension of the lowerradial bearing portion.
 4. The motor according to claim 2, wherein atleast a portion of the inertia portion and at least a portion of theupper radial bearing portion are arranged to radially overlap with eachother.
 5. The motor according to claim 4, wherein the inertia portion isarranged to have a mass greater than a mass of the flywheel.
 6. Themotor according to claim 4, wherein the flywheel is made of a resin,while the inertia portion is made of a metal.
 7. The motor according toclaim 2, wherein at least a portion of the inertia portion and at leasta portion of the lower radial bearing portion are arranged to radiallyoverlap with each other.
 8. The motor according to claim 7, wherein theinertia portion is arranged to have a mass greater than a mass of theflywheel.
 9. The motor according to claim 7, wherein the flywheel ismade of a resin, while the inertia portion is made of a metal.
 10. Themotor according to claim 2, wherein at least a portion of the inertiaportion and at least a portion of the upper and lower radial bearingportions are arranged to radially overlap with each other.
 11. The motoraccording to claim 10, wherein the inertia portion is arranged to have amass greater than a mass of the flywheel.
 12. The motor according toclaim 11, wherein the flywheel is made of a resin, while the inertiaportion is made of a metal.
 13. The motor according to claim 1, whereinthe inertia portion is arranged to have a mass greater than a mass ofthe flywheel.
 14. The motor according to claim 1, wherein the flywheelis made of a resin, while the inertia portion is made of a metal. 15.The motor according to claim 14, wherein the flywheel is an injectionmolded article produced with the inertia portion as an insert.
 16. Themotor according to claim 1, wherein the rotor hub includes: acylindrical portion arranged to extend in an axial direction, andarranged radially inward of the inertia portion; and a flange portionarranged to extend radially outward from the cylindrical portion axiallybelow the inertia portion, and a lower surface of the inertia portion isarranged to be in contact with an upper surface of the flange portion.17. The motor according to claim 16, wherein the inertia portion isarranged above the flange portion and below the flywheel.
 18. The motoraccording to claim 16, wherein the flywheel includes an innercircumferential surface arranged to be in contact with an outercircumferential surface of the cylindrical portion.
 19. The motoraccording to claim 1, wherein the rotor hub includes: a cylindricalportion arranged to extend in an axial direction, and arranged radiallyinward of the inertia portion with a gap therebetween; and a flangeportion arranged to extend radially outward from the cylindrical portionaxially below the inertia portion, and the flywheel includes aprotrusion portion arranged to protrude downward from a lower endthereof, and at least portion of the protrusion portion is arranged toradially overlap with the cylindrical portion and the inertia portion.20. The motor according to claim 1, wherein the rotor hub and theinertia portion are defined by a single continuous monolithic member.21. The motor according to claim 1, wherein the flywheel includes a wallportion arranged to cover at least a portion of an outer circumferentialsurface of the inertia portion.
 22. The motor according to claim 21,wherein the wall portion is arranged to cover the outer circumferentialsurface of the inertia portion from an upper end to a lower end thereof,and at least a portion of an outer circumferential surface of the rotorhub.
 23. The motor according to claim 1, wherein the flywheel isarranged to have an outside diameter greater than an outside diameter ofthe rotor hub.
 24. The motor according to claim 1, wherein the flywheelis arranged to have an axial dimension greater than an axial distancefrom a lower end surface of the stationary portion to an upper endsurface of the rotor hub.
 25. The motor according to claim 1, whereinthe rotor hub and the flywheel are defined by a single continuousmonolithic member.
 26. The motor according to claim 25, wherein thesingle continuous monolithic member is an injection molded article or acasting produced with the inertia portion as an insert.
 27. The motoraccording to claim 1, further comprising: a thrust bearing portion wherethe stationary portion and the rotating portion are arranged axiallyopposite to each other with the lubricating oil arranged therebetween.28. The motor according to claim 27, wherein the rotating portionfurther includes a thrust plate arranged to extend radially outward froma lower end of the shaft, and including an upper surface arrangedaxially opposite to a lower surface of the sleeve, the thrust bearingportion is defined between the lower surface of the sleeve and the uppersurface of the thrust plate, and a gap including the radial bearingportion and the thrust bearing portion is continuously filled with thelubricating oil.
 29. The motor according to claim 27, wherein the rotorhub further includes an annular portion arranged around the shaft, andincluding a lower surface arranged axially opposite to an upper surfaceof the sleeve, the thrust bearing portion is defined between the uppersurface of the sleeve and the lower surface of the annular portion, anda gap including the radial bearing portion and the thrust bearingportion is continuously filled with the lubricating oil.
 30. The motoraccording to claim 1, wherein the stationary portion further includes astator, the rotating portion further includes: a substantiallycylindrical magnet arranged to have a magnetic pole surface arrangedradially opposite to the stator; and a substantially cylindrical yokearranged radially outward the magnet, and the yoke includes a yokecylindrical portion arranged to cover an entire outer circumferentialsurface of the rotor hub and at least a portion of an outercircumferential surface of the magnet.
 31. The motor according to claim30, wherein the rotor hub includes: a cylindrical portion arranged toextend in an axial direction, and arranged radially inward of theinertia portion; and a flange portion arranged to extend radiallyoutward from the cylindrical portion axially below the inertia portion,the yoke includes a ring-shaped yoke upper plate portion arranged toextend radially inward from an upper end of the yoke cylindricalportion, and a lower surface of the yoke upper plate portion is arrangedto be in contact with an upper surface of the flange portion.
 32. Themotor according to claim 31, wherein the yoke cylindrical portionincludes: a first yoke inner circumferential surface to which an outercircumferential surface of the rotor hub is fixed; and a second yokeinner circumferential surface to which an outer circumferential surfaceof the magnet is fixed, the second yoke inner circumferential surfacebeing arranged below the first yoke inner circumferential surface, andthe first yoke inner circumferential surface is arranged radially inwardof the second yoke inner circumferential surface.
 33. The motoraccording to claim 1, wherein the rotating portion further includes amirror supported by the flywheel.